Heavy Drinking, Pot Use Tied to Teen Brain Changes

Teens who are heavily into drinking and smoking pot may show signs of breakdown in the brain's wiring system, a small study suggests.

Using brain scans of 92 teenagers, researchers found that kids who regularly drank and used marijuana showed negative changes in the brain's "white matter" over 18 months.

The brain has two broad types of tissue, known as gray matter and white matter. The gray matter can be seen as the brain's information-processing centers, while the white matter is like the wiring connecting those centers.

"White matter is the information highway. It allows the brain to communicate quickly and efficiently," said the study's lead researcher, Joanna Jacobus, a postdoctoral fellow at the University of California, San Diego.

If white matter is "less healthy," she explained, there could be subtle effects on a person's memory, attention and mental processing speed.

Dr. Duncan Clark, a researcher at the University of Pittsburgh School of Medicine who studies teen substance abuse, also weighed in on the study. "We are concerned that alcohol, marijuana or other substance use may cause delays or deficits in teen brain development," Clark said. "This study adds to those concerns."

The findings, reported online Dec. 14 in the journal Alcoholism: Clinical and Experimental Research, are based on 41 teenagers with a history of habitual drinking and pot smoking, and 51 teens who reported little, if any, alcohol or drug use. As a group, Jacobus and her colleagues found, kids who drank and smoked pot showed negative white-matter changes. In particular, the more they drank over the study period, the worse their white-matter integrity.